If a little base is added to an acidic solution and its pH changes from 3 to 4, what is the correct conclusion?
Answer and explanation
Correct answer: Acidity decreased but the solution is still acidic
The governing concepts are the pH scale and partial neutralisation. Both pH 3 and pH 4 are below 7, so the solution remains acidic. However, increasing pH by one unit means the hydrogen-ion concentration has fallen by a factor of ten: [H⁺] at pH 4 is one-tenth of that at pH 3. Therefore acidity decreased but did not disappear, making option A correct. It did not become a strong base.
Frequently asked questions
What is the correct answer to this question?
Acidity decreased but the solution is still acidic
Why is this the correct answer?
The governing concepts are the pH scale and partial neutralisation. Both pH 3 and pH 4 are below 7, so the solution remains acidic. However, increasing pH by one unit means the hydrogen-ion concentration has fallen by a factor of ten: [H⁺] at pH 4 is one-tenth of that at pH 3. Therefore acidity decreased but did not disappear, making option A correct. It did not become a strong base.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
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